Showing papers on "Radical ion published in 1968"

Electronic spectra of the free allyl radical and some of its simple derivatives

Abstract: Electronic spectra in the 2100–2500 A region, were reported for the allyl radical, the β-methallyl radical the α-methallyl radical, the β-ethallyl radical and the cyclopentenyl radical.The vibrational structures of the allyl and β substituted radicals indicate that in the main regions of absorption, the α(C—H) stretching frequency is excited. A single band progression observed in flashed allyl cyanide, was tentatively assigned to a free radical derived from pyrrole.

Electron spin resonance spectrum of the O–2 radical ion trapped in non-ionic matrices at 77 °K

Abstract: Trapped electrons are formed when alkali metal atoms are deposited on water or alcohols at 77 °K in the rotating cryostat. However, when trace amounts of oxygen are also admitted during deposition the deep colour and characteristic electron spin resonance (e.s.r.) spectrum of the trapped electrons are absent. Instead, the deposit is white and gives a highly asymmetric e.s.r. spectrum which has basically the same form in all of the solvents. However, the principal value g∥ of the g-factor varies slightly, but significantly, with the solvent in which the radical ion is trapped. Identical spectra in the corresponding solvents are observed from (a) frozen samples of water or alcohols which have been saturated with oxygen and then irradiated at 77 °K with cobalt-60γ-rays; and also from (b) samples which have been prepared by rapidly stirring sodium superoxide NaO2 into the solvent at room temperature and then immediately freezing the resultant slurry in liquid nitrogen (77°K). All of the e.s.r. spectra observed in these three groups of experiments arise from the O–2 radical ion which is trapped by an assembly of solvent molecules similar to the postulated for electrons trapped in the same solvents. The variation of g∥ with the solvent in which the radical ion is trapped is similar to that found for the energy of the maximum absorption in the optical spectra of electrons trapped in these solvents and reflects the degree of interaction between the ion and the solvent.

Fluorescence Quenching and the Charge Transfer in the Excited State. III. Flash Photolytic Studies

Abstract: It has been established by the flash photolysis that the N,N-dimethyl β-naphthylamine (DMN) cation is produced by the interaction of excited DMN with dimethyl isophthalate (DMP). The assignment has been made by comparing the transient spectrum with that obtained by the γ-radiolysis of DMN in s-butyl chloride. The decay of the DMN cation is first order in acetone (DK, 20.7), ethanol (24.3) DMF (36.7), second order in formamide (109.5) and it is the superposition of first and second order in acetonitrile. This strongly suggests that the radical cation exists as the solvent-shared ion pair in medium polar solvents while as free species in highly polar solvents. The decay of the former has been found to be not essentially affected by oxygen. The finding that the transient spectrum is observed even in the aerated solution supports the view that it is produced at the singlet excited state. From the effect of [DMP] on the yield of triplet DMN, it has been inferred that the radiationless process occurring in the ...

Studies of the Scholl reaction: oxidative dehydrogenation involving 1-ethoxynaphthalene and related compounds

Abstract: The oxidation of 1-ethoxynaphthalene and related compounds to give biaryl coupling products under a variety of Scholl reaction conditions has been investigated and the reaction mechanisms are discussed. The results are interpretable in terms of two complementary mechanisms, one involving conventional ionic intermediates and the other involving radical cation intermediates. Thus, mono- and meta-di-substituted aryl ethers are more likely to react by the radical cation pathway than by the ionic process whereas ortho- and para-di-substituted aryl ethers are expected to participate more readily in the ionic process. The oxidation of 1-ethoxynaphthalene with benzil and aluminium chloride in anisole solution has been shown to proceed through the intermediate formation of α-(4-methoxyphenyl)benzoin which causes the oxidation of the naphthyl ether to 4,4′-diethoxy-1,1′-binaphthyl while it is itself reduced to α-(4-methoxyphenyl)deoxybenzoin. This oxidative behaviour is also shown by α-phenyl- and α-(1-naphthyl)-benzoins; however, the intermediate formation of α-(4-ethoxy-1-naphthyl)benzoin does not lead to the formation of the binaphthyl ether but to the cyclodehydration product, 5-ethoxy-1,2-diphenylnaphtho-[2,1-b]furan. The significance of electron transfer processes in electrophilic aromatic substitution reactions is also discussed.

Electron spin resonance and optical studies of radiation-induced intermediates. Radical ions and radicals from α-methylstyrene in organic glasses

Abstract: Radical ion and radical intermediates derived from α-methylstyrene by gamma irradiation and photoionization in organic glasses have been assigned by e.s.r. and optical techniques. Measurements made in rigid solutions of the monomer in 3-methylpentane and methyltetrahydrofuran at –196° indicate that the radical anion is formed by electron capture during irradiation and exhibits absorption bands at 411 and 580 nm. When these glasses are warmed after gamma irradiation, the radical anion is converted to the neutral α,α-dimethylbenzyl radical by proton transfer from the positive ion. The latter radical is also observed in ethanol glasses immediately after irradiation, and the hyperfine splitting constants are 16.5 gauss for the 6 methyl protons and 5.5 gauss for the 3 protons (ortho and para) in the aromatic ring. Evidence from isotopic studies indicates that the neutral radical is formed in ethanol by proton transfer from the hydroxylic proton to the vinylidene group of the radical anion.

CHLOROPHYLL‐PHOTOSENSITIZED OXIDATION OF HYDROQUINONE AND p‐PHENYLENEDIAMINE DERIVATIVES

Abstract: — ESR and photovoltaic studies on light-induced one-electron transfer between chlorophyll a and electron donors in the absence of oxygen show (1) the possible conversion of photo-reduced chlorophyll a and p-benzosemiquinone ion radicals to their non-ionic radicals in methanol solutions of low pH, (2) the production of ESR absorption of tetrachloro-p-benzosemi-quinone even in benzene, enhanced by the addition of triethylamine or methanol, and (3) the transfer of one electron from tetramethyl-p-phenylenediamine to either excited chlorophyll a or pheophytin a in methanol at pH above 3.6 but not to pheophytin a at pH below 1 0 where its radical cation appears to accept an electron from excited pheophytin a. Bacteteriochloro-phyll is also shown to be capable of photooxidizing hydroquinones and tetramethyl-p-phenyl-enediamine. The presence of oxygen enhances chlorophyll a-photosensitized oxidation of hydroquinone and tetrachloro-hydroquinone by one-electron transfer to oxygen and of trimethylhydro-quinone probably by two-electron trnasfer to oxygen. A free radical from excited chlorophyll a-oxygen interaction is formed in these reactions, but rapidly quenched in the case of trimethyl-hydroquinone. This, kind of free radical is not formed in pheophytin a. Tetramethyl-p-phenyl-enediamine readily undergoes chlorophyll a-photosensitized oxidation by oxygen in any pH region.

Ionic condensation of olefins by ionizing radiation. Effects of additives and the detailed mechanism

Abstract: The mechanism of olefin condensation initiated by the radical ion, CnH+2n, is further supported by studies of the effects of additives on 1-pentene radiolysis. Radical scavengers inhibit formation of all of the dimeric products except 3-decene, formed with a G-value of 0.55. Electron scavengers in concentrations as low as 0.02 M increase this G-value up to a factor of 3; it is believed they interfere with ion-electron recombination and increase the ion lifetime. Proton scavengers and certain unsaturated additives at about 1 M reduce the G-value by competitive reactions with the olefin ion. Structures of the straight-chain ionic dimer indicate that ionic dimerization proceeds with carbon-carbon bond formation between terminal carbons, with a single hydride migration of an originally allylic hydrogen. Condensation to form trimer and higher polymers requires development of branching.

On the blue‐colored species, possibly assignable to a radical cation, formed by the aromatic hydrocarbon–sulfur dioxide–oxygen system: The polymerization of olefins initiated by aromatic hydrocarbons–oxygen in liquid sulfur dioxide

Abstract: It was found that styrene in liquid sulfur dioxide polymerizes, giving polystyrene readily and quantitatively by addition of such aromatic hydrocarbons as anthracene and trans- or cis-stilbene in the presence of oxygen, and the polymerization proceeds via a cationic process. The observations on the electronic spectra and kinetics in the system suggested that the polymerization was initiated by an electron transfer from the aromatic hydrocarbon to oxygen, followed by the formation of styrene radical cation. Supporting evidence of the radical cation is that 1,1-diphenylethylene in liquid sulfur dioxide in the presence of oxygen shows a peak at λmax = 605 mμ and reacts to give benzophenone and 1,1,3,3-tetraphenyl-butene-1, which are eliminated by addition of a radical or cation inhibitor.